State of the art techniques that are used presently for commercial production of carbon nanotubes show limitations in scale up possibility for large yields of fullerenes and CNT production, while the demand for CNT in emerging applications, for example in the field of materials is rapidly moving to the tons/month requirements.
Techniques such as the graphite arc methods that presently supply the carbon nanotube market (see U.S. Pat. Nos. 5,227,038; 5,482,601; 6,451,175 B1; 6,455,021; 6,063,243; and 5,753,088) are showing decreasing yields to nil as the arc power is increased, and poor energy efficiency. Other techniques such as laser ablation or chemical vapor deposition (CVD) techniques relate to methods that are not available at industrial scale power (Megawatt level) for providing yields above the grams/hour level.
An essential component of CNT growth is the provision of a method that provides for the nanometer sized metal catalyst particles acting as nucleation points for the tube growth. CNTs are typically formed when such nanometer size particles are present in systems generating fullerenes (C60, C70, and larger carbon cage structures). The catalyst prevents the closure of the carbon cage and enhances the growth of the long tubular structures. The graphite arc method typically introduces metal catalyst material within the solid graphite source with both carbon and catalyst metal being evaporated simultaneously. This results in difficult control of the carbon to metal vapor ratio, and no possibility of real time adjustments. Other methods use a long chemical route for assuring the presence of the nano-particles on surfaces on which the tubes are growing.